Adjustable speed capacitor motor



March 27, 1934. s. R. BERGMAN ADJUSTABLE SPEED CAPACITOR MOTOR OriginalFiled Dec. 9, 1932 Inventor'- Sven R. Bergman,

His Attorney.

Patented Mar. 27, 1934 UNITED it OFFICE ADJUSTABLE SPEED CAPAQCIEQRMIQTOR Sven It. Bergman, Nahant, Mass, assignor to General Electric()ompany, a corporation of New York .1 (Claim.

My invention relates to adjustable speed capacitor motors of the type inwhich capacitance is employed notonly to obtain split phase starting,but also for power factor correction during running, and the primaryobject is to provide a simple arrangement for maintaining a desirablevoltage upon the capacitance as the speed of the motor is varied. Thisapplication is a division of application Serial No. 646,466, filedDecember 9, 1932, assigned to the same assignee as the presentapplication.

It isknown that in the split phase type of motor having main andstarting windings with capacitance in the starting winding circuit, thevoltage across the starting winding and across the capacitance variesdirectly with speed. This is because of the variable transformer actionbetween the main and starting windings with various speeds and thedifference in the vector directions of the voltages across the startingwinding and the capacitance.

It is also known that the speed of this type of motor may be varied byvarying the voltage impressed upon the main winding. See, for example,United States Patent No. 1,726,231, Kennedy.

When the speed of such a motor is increased, it is desirable that thevoltage across the capaci== tance be decreased, and vice-versa, in orderto compensate for the variable voltage that would otherwise exist acrossthe capacitance due to transformer action; particularly is this truewhen speed variation is obtained by voltage variation across the mainwinding which acts as the primary of the transformer supplying thevoltage induced in the starting winding.

According to my invention, I provide speed regulating means whichautomatically changes the line component voltage across the startingwinding circuit in inverse ratio to the speed of the motor. Thus, whilean increase in speed increases the motor transformer voltage componentin the starting winding circuit, the line voltage component thereof isreduced. This arrangement not only prevents excessive voltages on thecapacitance during high speed running, but also tends to increase thecapacitance effect and motor torque for starting and low speedoperation, making it unnecessary, except in special cases, to provideother means for changing the amount 01' capacitance used. betweenstarting and running conditions.

The features of my invention which are believed to be novel andpatentable will be pointed out in the claim appended hereto. For abetter (6E. Elli-278) understanding of my invention, reference is madein the following description to the accompanying drawing, showing inFig. 1 a two-speed condenser motor provided with an auto transformer andspeed changing switch whereby the voltages applied across the main andstarting winding circuits are interchanged in value in the differentspeed adjustments. Fig. 2 represents voltage vector relations that willbe referred to in the explanation of Fig. 1. 6

Referring to Fig. 1, a. single phase condenser motor having main andstarting windings 10 and 11 is supplied from a line 12 or from a lowervoltage line 13 through an auto-transformer 1t. l'fhe motor secondary 15is shown as the squirrel cage type and as the rotor. 16 represents acondenser in the starting winding circuit, and 17 represents the speedcontrol switch.

it will be noted that the speed control device has two conducting parts18 and 19 mounted on the same movable arm, which is pivoted at itscenter. Part 18 is connected to one end of the starting winding 11 andcooperates with the two upper stationary contacts. Part 19 is connectedto one end oi the main winding 10 and cooper= 8i? ates with the twolower stationary contacts. The upper and lower stationary contacts tothe right are connected to the one end of auto-trans former '14, and theupper and lower stationary contacts to the left are connected to aninter- 35 mediate tap of the auto-transformer. The other ends of. themotor winding circuits and transformer are connected to line on theother side.

The connection with the speed regulating device in the position shown isfor starting and low speed operation. It is noted that the linecomponent of voltage applied to the main winding 10 is appreciably lessthan that applied to the circuit containing the stationary winding 11and condenserflfi. 'Under these conditions, with the motor operating atslow speed, we may represent the line component of voltage appliedacross the starting winding circuit by the vector A B in Fig. 2, andthat applied across the main winding by the vector C B. The voltageacross the start- 10 ing winding may then be represented by vector A D,and that across the condenser by D B. When the switch 17 is thrown tothe high speed position, the line component of voltage across thestarting winding circuit is reduced to C B, and that across the mainwinding is increased to A B.

I The voltage across the starting winding tends to increase due to anincrease in transformer action due to the increase in speed and the'mcreased voltage across the main winding acting as the,

primary or the motor transformer. However, due

to the reduced line component of voltage across the starting windingcircuit and the way the voltage vectors combine to close the voltagetriangle 5 of the starting winding circuit, the voltage across thestarting winding is not greatly increased, and may be represented by CD, while the voltage across the condenser remains about the same and maybe represented by D B. If, however, the line voltage component acrossthe starting winding circuit had been left unchanged as A B for highspeed operation, we would obtain a voltage triangle for the startingwindingcircuit of the order ,of A D B. This illustrates the advantage ofreducing the voltage across the starting winding circuit when the speedis increased in this way.

The invention provides good split phase starting conditions on the lowspeed point of the controller, since it will be evident that increasingthe voltage across a given condenser at start has the same eiTect asincreasing the amount of capacitance at constant voltage. Wherethestarting torque requirements are not excessive, the speed control switchmay serve as the starting switch, using the low speed position. Forheavy starting duty, it may be advisable to apply a higher voltage tothe main winding for starting, and facilities for accomplishing this maybe added without departing from the invention.

Such other modifications o! the invention as will occur to those skilledin the art for carrying out the invention are intended to be includedwithin the scope of the appended claim.

What I claim as new and desire to secure by Letters Patent 0! the UnitedStates,.is:

A two-speed motor having main and starting winding circuits, a singlephase source of supply, a transformer connected across said sourceindependently of the motor, connections between one end of both of saidwinding circuits and one side of said source, phase modifying meansincluded in the starting winding circuit, and switching means betweensaid transformer and motor for applying two difierent voltages to eachof the motor winding circuits in two different positions of saidswitching means such that the voltage applied to the main winding in oneposition 0! said switch is the same as the voltage applied to thestarting winding circuit for the other position of said switch, andvice-versa.

SVEN R. BERGMAN.

